Method and apparatus for measuring and calculating bulk water in crude oil or bulk water in steam

ABSTRACT

The present invention discloses an apparatus and method for continuous measurement of water volume in oil or steam which overcomes many of the shortcomings. In the present invention may shortcomings encountered in the prior art devices are overcome by placing a dielectric capacity probe inside the main pipeline, to measure the average dielectric constant (E) of the flowing mixture. This `in situ` sampling, will account for the entire cross-sectional area of the pipe or duct and its contents. The `in-situ` probe will have a high intrinsic capacitance approaching that of air, which has a dielectric constant equal to &#34;1&#34;. The probe placed within the pipeline shall offer a minimal impedance to flow of the crude oil or steam and the oil&#39;s normal impurities and sediments. The probe will automatically self-calibrate, `in-line`, at selected time intervals and shall be fully automated for the overall routine operation. Additionally it is an object of the present invention to continuously correct the measured capacitance as the temperature fluctuates throughout delivery.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/215,058 filed July 5, 1988, now U.S. Pat. No. 4,916,940.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for measuring thedielectric constant of a non-homogeneous mixture to determine theconcentration of various components in this mixture. Specifically theinvention relates an improved method and apparatus for measuring thedielectric constant of crude oil as it is transferred in order todetermine the percentage of water contained in the crude, or of water inthe liquid phase in a steam gaseous phase.

BRIEF DESCRIPTION OF THE PRIOR ART

Dielectric constant (E) measurements performed for the determination of`fractional volume` composition of two immersible fluids, have beenutilized for many years. Such dielectric methods are particularly usefulwhen it is necessary to distinguish different volumes of mixtures ofhighly varied dielectric constants (E's). Two practical applications ofthe method are:

1) Determining the proportion of water (W) to oil (O) `ratio` (W/O+W) inan oil pipeline or oil tank; since, the oil always contains minute tolarge quantities of water. The latter, being an amount of impurity of nocommercial value, and which, should be accurately deducted from thetotal `bulk volume` of delivered, purchased oil.

In a similar manner water volumes in steam can be evaluated to controlsteam quality during enhanced recovery operations by steam injectioninto heavy oil bearing strata.

2) At the well head, both water and oil are simultaneously produced.Probes, designated as "water cut" by design, using dielectricmeasurements, are run `downhole` (in situ) into the flowing well tocontinuously monitor, the ratio (W/O+W).

The key unit which provides such (W/O+W) ratio determinations is the`cylindrical capacitor`. The device has two electrodes whichautomatically measure the capacitance (Cd), and therefore, thedielectric constant (E) of the ratio (W/O+W) in the mixture, via twoelectrodes, against the `standard` E of the particular air capacitor.For example, the dielectric constant (E) of water (80 to 200-dependingdirectly on the salinity of the water) is significantly higher than thedielectric constant (E) of crude oil (2 to 3 depending on chemicalcomposition). Fluctuations in the ratio (W/O+W) vary directly with thedielectric constant (E). The properties and specific dielectricconstants (E's) of common and natural substances are available in mostelementary physical tables.

However, the above method of determining the ratio (W/O+W) is accurateonly if the tested mixture is homogeneous. Ideally, a homogeneousmixture contains uniformly dispersed, identical, macroscopic aggregates,of the chemically joined water and oil. These aggregates are considered,in theory, of the same fractional composition of ratio W/O+W as thesurrounding mixture.

Experience reveals that such homogeneity, in mixtures, does not alwaysexist. For example, in the first phase of discharging oil from a tankerat the oil terminal, water is the major fluid pumped out of the ship andinto the discharge pipe inlet. This occurs, because the intake pipe ispositioned on the floor of the ship's tank, where the water has settledduring transport at sea. The pumping of the crude/water mixturecontinues until the amount of water becomes less than 1% of the flowingvolume; thereafter the continuous discharge process enters therelatively longer duration second phase of pumping of the more undiluted(less water content), and commercially valuable crude oil. It is duringthis second phase of the discharging of oil, where the degree ofhomogeneity of the dispersed water-oil aggregates becomes ratherspeculative; and errors of C_(d) measurements and the concomitantevaluation of oil volumes raise serious questions, in regards toaccuracy.

A simple hypothetical model will serve to illustrate how the errors ofvolume analysis occur because of the erratic dispersion of water-oilaggregates.

According to designs presently used in the industry, the positiveelectrode of a cylindrical capacitor is a metal rod which is insertedalong the longitudinal axis of an in-line pipe; the pipe, the pipelineitself becomes the negative electrode of the capacitor. Four possibleconsiderations regarding identical volumes of water-in-oil are shown inFIGS. 1A,1B,1C,1D and 1E. FIG. 1A illustrates the electric equivalent oftwo capacitors connected in series due to the theoretical segregation ofthe oil and water. FIG. 1B illustrates the electric equivalent of twocapacitors connected in parallel due to the theoretical segregation ofthe oil and water. The terms, in series and in parallel are conventionalexpressions of basic electricity. FIGS. 1C, 1D and 1E represent threeadditional potential mixtures of water in oil which would result indistinct combinations of capacitors connected in a number of in seriesand in parallel configurations. It follows, that different spatialdistributions of the oil-water particles under identical quantities ofvolumes of oil in water, would yield different dielectric constants(C_(d) 's) and hence, different calculated volumes of fluid.

The prevailing system for measuring the dielectric constant (C_(d))during the above mentioned second phase of the discharge process, isrepresented in FIG. 1E. The inherent shortcoming of this measurementsystem is due to the random heterogeneous dispersion of the minusculewater droplets across the cross-sectional area of pipe, where theelectrodes are placed. In this imprecise condition the measurement offractional volumes of water in oil, is far less than ideal; and still,the precision of this measurement is of utmost importance in everydaycommercial transactions.

In recognition of the need for precise, consistent, reliable andexacting measurement systems, apparatus and methods have been devised toovercome the apparent problems of determining, precisely, the fractionalvolumes of water in oil.

Present methods of water in oil determinations use `intermittent`sampling. Their complex approach is to:

1) Collect samples (via an in line tap), of the oil and water mixturefrom within the pipe, in sections of the line where fluid homogeneity islikely to exist, i.e. areas of turbulence, or eddies, created by bendsor elbows in the pipe system.

2) Collect such samples at regular intervals of time.

3) Divert the sample to a conventional capacitor cell, and measure thecapacitance (C_(d)) of the mixture.

4) Remove the water from the mixture by means of a centrifuge.

5) Again measure, in the capacitor cell, the capacitance (C_(d)) of thewater-free oil.

6) Compare the values derived from steps 3) and 5) to determine thewater volume in the mixture.

Several weaknesses of this technique are however inherent and must beexamined.

A) It is imperative that the homogeneity of the sampled mixture directlyreflect that of the source fluid mixture. Since this condition does notexist, an unknown factor exists in these methods, as to how perfectlythe homogeneity of the sample matches that of the sampled fluid.

B) It follows, that a continuous monitoring of the fluid would give moreaccurate dielectric constant (E) measurements, viz-a-viz intermittentsampling; since, particulate dispersion configurations of the sourcemixture, will very likely change, between samplings.

C) Additionally these methods have no way of accounting for variationsin temperature of the fluids. These temperature variations create anadded complexity which must be accounted for.

A much more accurate method has been developed by Shell Oil Company. Theaccuracy of the water in oil evaluation is highly improved by conductinga continuous sampling of the pipe flow, rather than intermittentlysampling the oil as previously described. Another method of determiningthe dielectric constant (E) in oil-water mixtures was developed by`Endress and Hauser` in a joint effort with British Petroleum. Thatmethod is described as follows:

1) A small diameter by-pass pipe loop is diverted from the main pumpingpipe. The loop contains a coaxial lead, which serves as the positiveelectrode of the cylindrical capacitor. The loop, itself, is thenegative electrode of the capacitor.

2) Measurement of dielectric constant (E) is taken directly from theby-pass loop.

The `Endress` system has an advantage in improved accuracy in that

A) Sampling is continuous, (as opposed to intermittent).

B) A greater degree of homogeneity of the sample is achieved, becausethe smaller diameter by-pass creates increased flow velocity (Venturi'seffect) with a consequent increase in turbulence and shear forces(mixing) of the fluid.

C) The constricted by-pass, reduces the space between the capacitor'selectrodes. Since interelectrode distance is inversely proportional tocapacitance, i.e. the shorter the space the greater the capacitance, agreater accuracy of dielectric constant (E) measurement is possible.However, temperature fluctuations, hence, mathematical corrections, arenecessary for an accurate determination of the dielectric constant (E).

Both the `Shell` and `Endress` methods of measuring dielectric constant(E) fail to account for the variations of the dielectric constant whichare due to the assumption that the sample (drawn for the test) is arepresentative sample of the fluid volume flowing thru the pipe.Measurement systems which assume that the sample is representative ofthe fluid volume flowing in the pipe are inaccurate since they rely onassumptions which typically are not encountered since the sampleremains, de facto, only a small fraction of diverted fluid. Additionallythese measurement systems become more complex because necessary periodicrecalibrations are required in the laboratory, to account for thedifferent dielectric constants (E values) which vary with density andchemical composition of the crude oil collected by the tanker en routefrom different fields. These recalibrations are performed, using thesame cumbersome sampling and separation process(es) described above.

In steam injection control, no method seems to be considered reliablefor consistent practical application. The techniques available sufferfrom such shortcomings as lack of representativity and dispersionpattern errors as the ones encountered in water in oil mixtures.

SUMMARY OF INVENTION

It is an object of the present invention to provide an improved methodof continuously measuring the dielectric constant (E) and thusovercoming the observed difficulties arising from a heterogeneousmixture of water in oil or in steam. It is a further object of thepresent invention to recognize the non-homogeneous nature of crude oilor steam deliveries and disclose an invention which does not rely on agross assumption that the water in oil or in steam mixture ishomogeneous and unaffected by temperature.

It is a further object of the present invention to obviate the necessityof time consuming `recalibrations` which are typically performed in alaboratory to calibrate an instrument under ideal conditions for servicein conditions which are less than ideal.

It is a further object of the present invention to disclose an apparatusand method for continuous measurement of water volume in oil or in steamwhich overcomes many of the shortcomings of the prior art methods whichonly sampled a small cross section of the volume.

It is a further object of the present invention to apply the presentstructure for measuring dielectric constant (E) to substances other thanwater in oil; the latter being a notable example because of its widerange of application and economic importance.

It is a further object of the present invention to overcome theshortcomings encountered in the prior art devices by placing adielectric capacity probe inside the main pipeline, to measure theaverage dielectric constant (E) of the flowing mixture. This `in situ`sampling, will account for the entire cross-sectional area of the pipeor duct and its contents. The `in situ` probe will have a high intrinsiccapacitance approaching that of air, which has a dielectric constantequal to "1". The probe placed within the pipeline shall offer a minimalimpedance to flow of the crude oil or steam and the oil's normalimpurities and sediments. The probe will automatically self-calibrate,`in-line`, at selected time intervals and shall be fully automated forthe overall routine operation. Additionally it is an object of thepresent invention to continuously correct the measured capacitance asthe temperature fluctuates throughout delivery.

One of the unique and novel aspects of the present invention is that theprobe is to be mounted inside the main line and substantially fill theentire cross-sectional area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D and 1E illustrate five possible distributions ofwater in oil which may be encountered in a pipeline in typicaloff-loading operations.

FIGS. 1AA and 1BB illustrate electrical equivalents of FIGS. 1A and 1Brespectively.

FIG. 2A illustrates one of the preferred embodiments for the presentinvention depicting long, thin and narrow metal `plates`, each connected`in-parallel`; and, each having alternatively `assigned` `positive` and`negative` polarities. For the sake of simplicity, only four plates areshown.

FIG. 2B illustrates an equivalent circuit for the embodiment illustratedin FIG. 2A.

FIG. 2C and 2D illustrates another embodiment of the present inventionillustrating the capacitor plates installed in a square or rectangularcross-section of a pipeline, with FIG. 2C illustrating a homogeneousdistribution of water in oil and FIG. 2D illustrating a non-homogeneousdistribution of water in oil commonly associated with the initialtransfer phase or an non-turbulent condition.

FIG. 3A illustrates one method of isolating the positive from thenegative plates at the time the capacitor network is installed in apipeline. FIG. 3AAA also illustrates the type of instrumentation whichis required to measure the capacitance within the capacitor network andconsequently the dielectric constant of the fluid within the pipeline.

FIG. 3AA is a cross-section of FIG. 3A.

FIG. 3B illustrates the typical location of the capacitor network shownin FIG. 2D in a square or rectangular cross-section of a pipeline.

FIG. 4 illustrates the correlation between the dielectric value and thepercent of water for seven crude oils.

FIG. 5 illustrates an innovative method of calibration which requiresthe injection of a known quantity water into the crude.

FIG. 6 illustrates some of the values which were extrapolated from FIG.4) to compare the range of the fluid capacitance values during the`first` and `second` phase of the discharge process.

FIG. 7-A (and FIG. 7-B, for its equivalent circuit) illustrate theapproximate placement of concentric plates in a circular cross-sectionof the pipeline and an equivalent circuit for the concentric placementof the capacitor plates (in this case, the unequal gaps between platesinsure identical volumes between each set of 2 contiguous plates).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One of the objects of the present invention is too overcome many of theproblems encountered by prior art methods and apparatus in themeasurement of water content in crude oil or in steam. This and otherobjects of the present invention will be described herein. Although thepreferred embodiments relate to specific physical configurations forplacement of capacitor electrodes, this invention is not limited to anyspecific physical geometric configuration.

To overcome some of the short-comings of the prior art devices thepresent invention overcomes the difficulties arising from heterogeneoussampling of water in oil or steam mixtures. The present inventionprovides for more accurate results while at the same time minimizing thenecessity for time consuming recalibrations which by necessity areperformed in the laboratory. Additionally the present invention achievesthe goal of providing continuous measurement of water volume in oil orsteam over the whole delivered bulk mixture.

It should be noted, that the method and apparatus disclosed herein formeasuring the dielectric constant (E) may equally apply to substancesother than water in oil or steam, however, the latter are a notableexample because of its wide range of application and economicimportance.

A unique feature of the proposed invention is that a capacitor array isto be mounted inside the main line in a manner which substantially fillsthe entire cross-sectional area of the pipeline. This is the equivalentof a large number of very small elementary capacitors, of identical aircapacitance. These units are connected electrically, in-parallel, in asymmetrical pattern; wherein, each capacitor contains the same volume ofdielectric material between its individual electrodes (or plates).

One of the shortcomings of a concentric arrangement of capacitor platesin a circular cross-sectional area is that the capacitance is unequalfor equal distances between plates due to the increasing circumferenceof the plates. Thus the volume of dielectric material between the plateswill vary as a function of the circumference of the plates. Thisshortcoming can be overcome by reducing the spacing between the platesas the circumference is increased.

To implement the configuration set forth in FIGS. 3A or 3B, it isnecessary to use long, thin and narrow metal plates, each connectedin-parallel; and, each having alternatively assigned positive andnegative polarities, as illustrated in FIG. 2A, (for the sake ofsimplicity, only four plates are illustrated).

To establish the electrical equivalency of the long, narrow, plates andthe large quantity of small capacitors, FIG. 2B is a hypotheticalrepresentation of each plate, which is split into a larger number ofinterconnected smaller plates. In summary, both FIG. 2A and FIG. 2B areelectrically equivalent, as is obvious to those of ordinary skill in theart.

An arrangement of capacitors such as that illustrated in FIGS. 2A, 2Band 2C functions as a sensor to the fluid within the entire pipecross-sectional area; and, will contain its own dielectric (oil, wateror both) because all of the capacitors are identical and connectedin-parallel. Additionally the total capacitance of the particularconfiguration is the sum of the smaller individual capacitances, thetotal measured capacitance will represent the average of all the smallercapacitances contributing to the measurement.

Expressed mathematically:

C=The intrinsic capacitance of each small (elementary) capacitor.

E₁ =The dielectric constant of capacitor #1.

E₂ =The dielectric constant of capacitor #2.

E₃ =The dielectric constant of capacitor #3.

E_(n) =The dielectric constant of capacitor #n.

C_(t) =The capacitance of the number of capacitors connected inelectrical parallel.

Thus:

    C.sub.t =C.sub.E1 +C.sub.E2 +C.sub.E3 +..........C.sub.En.

    C.sub.t =C.sub.(E1+E2+E3+..........En).

    C.sub.t =C×(the average dielectric constant (E) of the fluid mixture of the pipe cross-sectional area).

If the dielectric fluid in the pipe is water only, C_(t) is maximum:

    C.sub.t =C×n×E.sub.water

If the fluid is oil or steam only, then Ct becomes minimum:

    C.sub.t =C×n×E.sub.oil

    or C.sub.t =C×n×E.sub.steam

For mixtures of oil or steam and water,, C_(t) values will be betweenboth maximum and minimum of the above. In summary, C_(t) will reflect an`average` of the fractional water volumes of the mixture flowing througha array of plates which cover the entire inside cross-sectional area.

Several arrangements of these small plates connected in-parallel arepossible. For simplicity a square or rectangular design will be used toexplain the unique aspects of this system for measuring capacitance andconsequently water content in oil or steam.

The parallel plates within the capacitor array or network are assembledin a manner which substantially traverses the cross-sectional area of aduct. Preferably the duct is square or rectangular in shape, howeverother equivalent geometrical configurations are also envisioned. Theduct is fitted in a manner such that it is in-line to pumping pipecarrying the fluid to be measured for water content and is held in placewith appropriately designed couplings or pipe flanges. Although relativesize is not of primary importance, the duct cross-sectional area shouldbe smaller than the pipe, so as to increase fluid velocity, turbulence,mixing and homogeneity.

Another design, which avoids the use of a duct, would be to insert thesquare array of plates directly into the circular pipe via an elongatednarrow window, peripherally sealed and parallel to the pipe'slongitudinal axis.

A detailed example of such an assembly is illustrated in FIG. 3A. FIG.3A depicts one embodiment of the present invention and is not intendedto limit the scope of the present invention.

In FIG. 3A, narrow elongated metal plates or rods (or other comparablegeometric configurations suitable for use as capacitor plates)[hereafter all collectively referred to as plates] 1 are attached atattachment point 3 by means of welding or some other comparableattachment means which produces a low-conductivity path or short-circuitto insert 2. Each plate or rod 1 and its associated insert 2 is thencoated with a layer of hard electric insulating material, such asdielectric tape or enamel or other comparable insulating material. Theinserts 2 are then inserted into a narrow, elongated, perforatedrectangular cover 4 which is constructed of a hard, non-hydroscopic,non-conductive material, such as fiberglass or polyvinyl chloride (pvc).The design is of very high tolerances, achieving a close of fit betweenthe inserts 2 and the perforation 5 of cover 4. The cover 4, hasclamping `shoulders` 4a (in the illustrated configuration) to allow theunit to be sealed and bolted to the pipeline or fluid duct 13. Eachplate or rod 1 is installed in a manner such that the rod or plate 1 issubstantially perpendicular to the cover's longitudinal axis (x--x'),see top view. The plates are secured to the cover by close fitting`locking pins` 6 which are inserted in the conforming counterpart pinholes 6a in insert 2. Inserts 2 are alternately interconnected toconducting bars 7. These conducting bars 7 are arranged in such amanner, that the odd numbered plates 8 are electrically connectedtogether, but electrically isolated from the similarly installed evennumbered plates 9. The completely interconnected odd numbered plates 10become, in effect, the positive electrode (or plate) of a workingcapacitor. Similarly the interconnected even numbered plates 11 becomethe negative electrode (or plate) of a working capacitor and areconnected by a lug (12) (or any other conventional means) to the body ofthe pipe, which is at ground (earth) potential and is the `negative`electrode of the capacitor.

To minimize surface corrosion and galvanic activity between the lockingpins 6 and the counterpart pin holes 6a of the inserts 6 and to insuredependable electrical contact between the locking pins 6 and thecounterpart pin holes 6a of insert 2 the pins 6 and inserts 2 should beconstructed of similar metals.

The completed assembly described above, is to be inserted into a pipe orduct 13 positioned such as to cover the duct's entire cross-sectionalarea. Although a square or rectangular duct 13 is illustrated thisfeature is not viewed as a particular limitation of the presentinvention. The duct 13 consists of a rectangular window 14 which isslightly wider than the cover width "w", (illustrated in the side viewof FIG. 3A) of the wall of the duct. The shoulders 4a of cover 4 aresecured to the duct's flange 15 with a series of bolts, nuts and washers16, which are conventional in design within the piping industry. A flatrubber washer 17 is positioned between the cover's shoulders 4a andflange 15, to insure a reliable seal between the two machined metalsurfaces.

The opposite end of each plate or rod 18 is attached to a thin, flat,hard, rectangular insulating strip 19 which is constructed of the samematerial as that used for the cover 4. Inserting the plate or rod ends18 with narrow, parallel grooves 21, machined into the strip's face,will enhance the adhesion of the plate ends 18 to the strip 19. Annon-conductive adhesive 20 is used to adhere plate ends 18 to strip 19.Further uses of the word adhesive will refer to any material, i.e. epoxyresin, that has the properties of a chemical fastener or substance thatcan, by application, render an object impermeable to gases and/orfluids).

A flat, thin sheet of soft rubber 22, dimensionally identical to strip19 is joined to the reverse face of the strip, using an adhesive. Therubber 22 functions as a seal between the strip 19 and duct wall, andalso increases the mechanical resiliency of the strip 19.

With the plate spacings between plates substantially equal andsubstantially identical spacings existing between the outboard plates 23and 24 and the duct's wall 13, then the capacitor and its specificarray, may be considered complete in construction.

The ends 25 of the insert 2 are coated with an adhesive 26 which sealsthe assembly against fluid leakage from the inside and through theinterface 27 between the inserts 2 and the perforated walls 5 of cover4. Under normal conditions, the pressure differential between the insideof the pipe and atmosphere is quite low; therefore, this simple methodof sealing should be sufficient against leakage. Should conditions of ahigh pressure differential be encountered, the design can be easilymodified by using conventional O-ring seals (28) as well as othersealing methods well known in the art.

The configuration illustrated intentionally limits the occurrence ofstray (i.e. `inter-rod`) capacitances, by minimizing areas andmaximizing gap widths. The effect of the enamel coat on the plates isminimal because of its thin coating applied and the fact that the enamelis electrically equivalent to a high stray capacitance, connected inseries, to the measured capacitance and considering that the reciprocalsof capacitances add in the series connected mode.

In design and function, the capacitor has two important variables. Theseare:

1) The width of the plates 1 designated as "w_(p) ".

2) The gap between the plates "g".

The wider the `w_(p) `, and the narrower the `g`, the greater, becomes,the overall capacitance of the array of plates. This results in a largernumber of small equivalent capacitances and better resolution of themeasured signal.

One of the inherent shortcomings of the above-described configuration isthe development of a proportionally greater in-line resistance to fluidflow. Therefore, a balance must be attained between `w_(p) ` and `g` toachieve optimal electrical and mechanical results. A practical examplewill demonstrate how such calculations can be formulated:

The example assumes that a housing with a total cross-section of threesquare feet, one inch wide "w_(p) " plates separated by a one-half inchgap (g), would provide an intrinsic capacitance of approximately 400picofarads. This minimal capacitance insures a quantitative andqualitative resolution of measurement of signals above electrical`noise` levels, with minimum resistance to `in-line` fluid flow.

With this unique design, several options are available for monitoringchanges in fluid capacitance flowing through duct 13. Commercially,Hewlett-Packard (H-P) manufactures several highly sensitive and accurateinstruments which can be integrated into the system. For example an H-Pmodel 4278-A would be an acceptable capacitance meter to measure thecapacitance encountered by parallel plates within duct 13.

Another comparable means of measuring the capacitance of the plateswould be to arrange the electrical circuitry such that one of theelements can function as a precise bridge 29. The bridge input may bepowered by an oscillator (30) such as an H-P Model 3314-A, which isnoted for its versatility, accuracy and dependability. The bridge outputis a frequency signal (f) which is directly proportional to the squareroot of the capacitance (C) of the described array and can be calculatedas follows:

    f=k/C.sup.1/2                                              (1)

where k is a constant derived from components of the bridge.

To determine the frequency of the measurement a high resolutionfrequency counter 31, such as an H-P Model 5314-A is connected at theoutput of the bridge. This instrument may be used to send the varyingmeasured frequencies to a computer terminal 32 which may be used toconvert the measured electrical signals directly into values offractional water volumes. The latter would be electronically displayedon a display 33 after appropriate processing and conditioning of thesignal to permit display on such displays as seven segment display,light emitting diodes, fluorescent tubes or liquid crystal cells.

In the alternative the dielectric constant can also be determined bymeasuring the phase shift of the frequency in lieu of determining theabsolute frequency by means of a counter or other method.

The computer 32 includes a water totalizer, which integrates (over time)the instantaneous fluctuations in water volume. This integrated (ortotalized) value may the be recorded on a commercial strip chartrecorder 34, such as H-P Model 7090-A ("Plotter-Recorder"). All measureddata may be stored on common disks or tape.

Due to minute variations in tolerances between units, each capacitorarray requires calibration in the laboratory. This initial calibrationis conducted in dry air, which has a minimum dielectric constant (E)of 1. Should other dielectric material fill the inter-plate gap, thecapacitance of the array will increase. A maximum value of E is attainedwhen the substance is 100% water.

It is recognized by the petroleum industry, that the range of interestin ratio of water to oil (W/O+W), in the practical deliveries of crudeoil is 0.0% to 1.0% whereas for water in steam this range is 0.5 to 3%.Precisely conducted tests of E on various oil and water mixtures (allwell homogenized, and of various geographic origins) have been publishedby British Petroleum (BP). These results are described by the curveshown in FIG. 4. Illustrated in FIG. 4 are the variations of watervolumes in percent (%) versus the average crude's dielectric constant(E), in the range of zero to 50%. It is important to note that thiscurve is linear in the lower range, i.e. 0% to 5%.

Independently and without reference to the study by BP, the applicant'sinvention arrives at the same conclusions and establishes numericalagreement with the data published by BP. The applicant uses an algorithmwhich was derived from a mathematical model published in 1914 by K-WWagner, (Arch. Elektrotech. 2, 378). This model, called theMaxwell-Wagner Model, evaluates the dielectric constant (E) of asuspension of electrically conductive particles of small diameters in anon-conductive dielectric medium. The Maxwell-Wagner model correspondsexactly to the oil and water or steam and water mixtures encountered inpractice.

As the Maxwell-Wagner model requires, it is first legitimate to modelthe mixture as spherical droplets of water dispersed in a continuousphase of oil or steam. Text books of physics state that a immersedliquid assumes, under its surface tension, a shape that offers theminimum area to the surrounding fluid; this shape is a sphere.

The Maxwell-Wagner equations imply that neither the size of the waterparticles, nor the magnitude of their electric conductance (or salinity)and dielectric constant (E), or their dispersion patters have anybearing on the bulk dielectric constant (E) of the mixture in the lowwater volume range. These physical facts are confirmed by thepublications of BP.

Besides, the Maxwell-Wagner model assumes, as a primary condition forits validity, that the electric field to which the mixture is submitted,is constant. This condition fits perfectly the parallel plate capacitorsince this field is constant according to the electrostatic theory. Italso fits, but not perfectly, the cylindrical capacitor designed byEndress-Hauser under BP sponsorship, since the inter-electrode gap is sothin that the electric field therein is almost constant (in cylindricalcapacitors, the inter-electrode field varies as the inverse of thedistance from the inner electrode, small gaps between electrodes meansalmost constant distance from the inner electrode therein.)

Under a constant electric field, it can be demonstrated that the globaldielectric constant of the inter-electrode mixture is independent of thegeometry of the spatial distribution (dispersion pattern) of the waterdroplets dispersed in the continuous phase, that is oil or steam.

To achieve this independence of mixture dielectric constant fromdispersion patterns, Maxwell-Wagner state that the distance betweenspheres must be large compared to their radii. This applicant hascalculated that this condition is fulfilled at water fractional volumesof 5% or less. This figure is compatible with the range of small volumesof water to be evaluated either in oil or in steam. The Maxwell-Wagnermodel is therefore legitimate.

In the range of zero to 5% of water volume in an oil-water mixture, thelinear relation between the fractional water volume (V) and themixture's dielectric constant (E) is expressed by the followingequation:

    V=1/3×(E/E.sub.oil -1)                               (2)

where E_(oil) is the dielectric constant of the crude oil being measured

Alternatively E_(steam) should be substituted to E_(oil) in steam watermixtures.

Combining equations (1) and (2), the calculation to be performed by thecomputer 32 can be expressed as follows:

    V=(K/E.sub.oil ×f.sup.2)-1/3                         (3)

where K is a constant equal to k² /(3×air capacity of the array)

The dependence of `V` on `E_(oil) ` is obvious from equation 2).`E_(oil) ` varies with crude density, chemical composition andtemperature. This latter fact, creates the necessity for constantmonitoring and measuring the E_(oil), and reveals the wide range ofapplication of the present invention in the petroleum industry.

On the other hand, the dielectric constant of steam if always "1" (one)and independent of temperature and pressure, under the conditionsassociated with steam injection operations.

To minimize the need to calibrate the system by employing prior-artsampling and remeasurement of the flowing crude, an innovative method ofrecalibration is disclosed and illustrated in FIG. 5. For steam-watersystems this calibration method is not necessary as E_(steam) =1 forsteam injection operations. This method is not viewed as necessary topractice the present invention as only an initial dry (in-air)calibration is necessary to satisfactorily operate the array. However insteady-state flow conditions when a transient may be necessary tosatisfy operating personnel that the system is working properly thefollowing calibration procedure is recommended.

In the preferred embodiment the capacitor array is located in ahorizontal section of the crude oil pipeline for measuring the watercontent during the initial transfer phase, and another capacitor arrayis located in a vertical section of the crude oil pipeline for measuringthe water content during the stable transfer phase. In the alternativeone capacitor array may be used in either a vertical or horizontalportion of the pipeline, however the use of only one capacitor arraywould yield accurate results during only one phase of the transfer, e.g.a horizontal array would yield accurate results during the initialtransfer phase and a vertical array would yield accurate results in thestable transfer phase. A combination of both a vertical and horizontalarray permits one to optimize the system to obtain accurate resultsthroughout the complete transfer of crude from the tanker to theon-shore storage facilities.

For the array located in the horizontal section of the crude oilpipeline it is advisable to locate the array a few pipe diametersdownstream of the transition of a circular pipe or duct to a rectangularpipe or duct. Additionally the transition from a circular pipe or ductto a rectangular pipe or duct should be designed in a manner to minimizeturbulence and stabilize the oil-water interface level by enhancingsegregation.

This horizontal mode configuration takes advantage of the naturalsegregation of the water at the bottom of the duct under the gravityforce field.

In crude oil applications, the algorithm for solving for "V" under thishorizontal mode operation is different from the one applicable to lowwater fractional volumes described by equation 2,). Equation 2 shouldrather be used as follows:

    V=(1/(E.sub.w /E.sub.oil -1))×((E/E.sub.oil -1))     (2')

In crude oil applications, E_(w) is the dielectric constant of theflowing water, which is no longer negligible as in Equation 2, as wateris present in very large quantity, compared to oil. If V=1, the measuredE is equal to E_(w).

As the water content of the oil/water mixture decreases, it would beadvisable to install, as show in FIG. 3, two parallel plate (singleelement) capacitors, one at the floor of the crude oil duct to monitorthe dielectric constant of the water, one at the ceiling of the crudeoil duct, to monitor the dielectric constant of the oil, both fluidsbeing, as we know, segregated by gravity forces, under conditions ofhorizontal flows. These two fundamental data points will be availablefor the processing of the second phase.

For the array located in vertical section, it is advisable to locate thecapacitor array in a vertical section of pipe 35, preferably downstreamfrom an elbow or bend 36, where greater turbulence improves thehomogeneity of the crude/water mixture.

Referring now to FIG. 5 and specifically applicable for calibrationpurposes, in crude oil applications, upstream from 36 a water injector37 is inserted inside the pipe, with its injector head 38 located at thecenterline of the pipe. A pump 39 injects water intermittently duringselected time intervals. The pump action is directed by a typicalindustrial controller 40. The input signal to the controller 40 comesfrom a flowmeter 41 which sends an electrical signal directlyproportional to the rate of flow inside the pipe. The controller outputinstructions direct the pump to inject water into the crude flow, afractional volume (V_(o)) of water. Under such conditions, the frequencyoutput from the counter 31 changes from value `f` to a new value `f_(o)` and equation (3) can be rewritten as:

    V+V.sub.o =(K/(E.sub.oil ×f.sub.o.sup.2))-1/3        (4)

Eliminating `V` from equations (3) and (4) yields:

    E.sub.oil =(K/v.sub.o)×(1/f.sub.o.sup.2 -1/f.sup.2)

The computer 32 performs the necessary calculations and based on theforegoing equations and enters the new calculated value of E_(oil) intoequation (3).

The water injection rate, duration and quantity are determined by localconditions. For example, if the type of crude oil and its temperatureare expected to be relatively stable, limited control only, may berequired, (in such cases, it may even be performed manually). Note thatthe newly derived value of E_(oil) is automatically corrected fortemperature; thus, obviating the need for temperature control. In someinstallations, water injectors are already installed for periodicalcalibration checks.

It is advisable to monitor the entire discharge operation (from the shipto the storage tanks) beginning with the first phase; wherein,appreciably more water than oil is drawn into the `inlet pipe`.Subsequently, a more accurate and efficient evaluation of the water tooil ratio (W/O+W) of the bulk of the cargo is achieved. The curvesdescribed in FIG. 6 (which were extrapolated from those in FIG. 4),compare the range of fluid capacitance in values during the `first` and`second` phase of the discharge process. Note that if the range ofinterest in water volume evaluation is set to a maximum of 1%, thiswould correspond to an approximate dielectric constant (E) in the narrowrange of 2 to 2.4. In the high water volume range, the dielectricconstant (E) of the fluid is highly dependent on the salinity of thewater. It is, therefore, advantageous to begin early monitoring ofdielectric constant (E) during initial discharging of the crude oil, sothat an accurate evaluation of the gross amount of water can bedetermined, before the critical 1% fractional water volume is attained.Thereafter, the precise measurement of water volumes in the second phasewould be determined by computer program as previously described.

In the event that a single mode vertical operation is desired,implementation of a calibration curve such as the ones shown in FIG. 6in the high water content range, is necessary. Initial values ofdielectric constants of the water and oil involved in the flow, must beknown, since the calibration curve is dependent upon temperature andwater salinity. These values are obtained from laboratory analysis ofin-line collected samples or in the alternative by the single elementcapacitors installed at the top (for oil dielectric) and the bottom (forthe water dielectric) of the material contained in the pipeline upstreamof the capacitor array.

Since the calibration curve is non-linear; conventional methods ofnumerical analysis should be used in order to program the computer in anappropriate manner. Straight or curved segments approximation equationsare two of such methods. The computer program outputs the value "V" ofthe function, from the processing of the input variable "E".

Continuous temperature monitoring is recommended and subsequent fluidresamplings may be necessary, until the injection process for automatedrecalibration is initiated.

Errors due to non-homogeneous fluids should be expected; for thisreason, the horizontal mode of operation during the first phase of crudeunloading is recommended, not only on account of its accuracy, but alsoon account of the relative simplicity and efficiency of the method usedin handling the data.

The procedure continues, until the 1% water volume is detected;thereafter, the computer is then programmed to obtain:

1) Accurate water in oil evaluations and to

2) Periodically inject water for recalibrations of the capacitor array.

Prior to reaching the 1% detection level, a sample of crude is collectedthrough the same shunt as the water sample, mentioned above for theprior art devices. The water is removed from the sample in thelaboratory, and its E_(oil) value is measured in a conventional cell.After this initial E_(oil) is entered manually into the computerprogram, the automated monitoring process can begin. Estimates are thata capacitor bridge design operating at a frequency of 100 kilohertzwould maintain a sensitivity of about 14 hertz for every incrementalwater volume in oil of 0.01%.

The whole process would be enhanced by the use of static mixers, mountedin-line and upstream from the monitoring instrumentation. Komax,manufactures such a mixer which requires no external power to operate,however such mixer introduce a minor pressure drop due to therestriction imposed on the flow. With a mixer such as that suggestedturbulence and the concomitant homogenization of the crude are createdby the geometrical configuration of the mixing elements themselves.

Between oil deliveries or steam injection operations, the capacitorarray can be removed from the line, cleaned and recalibrated in `dryair`. A dry air, condition can be achieved by using a blow torch orother heating device. The bridge and associated electronics can bechecked against a fixed capacitor of known value.

As previously mentioned, a rectangular or square duct housing an arrayof parallel plates is but one of several possible electrodeconfigurations which will satisfy the requirements for obtainingidentical capacitances and measuring dielectric volumes. However, otherconfigurations may be selected to practice the present invention.

The embodiment show in FIGS. 7A and 7B is attractive in that cylindricalcapacitors conform to pipeline cross-sections which are circular,however, when concentric cylindrical capacitor plates are used, it isvirtually impossible to achieve equality of elementary volumes andcapacitances as in the case of parallel plates; one suffers at theexpense of the other. Under such conditions, design simplicity andminimal encumbrance are achieved at the cost of measurement accuracy.

Even though identities of capacitances and dielectric volumes may beachieved for all capacitors, unlike the parallel plates pattern in arectangular duct the shapes of the capacitors cannot be superimposedsince each capacitor's gap decreases as the pipe radius increases (withcorresponding increases in circumferential lengths). Therefore, theuniformity of distribution of elementary capacitors is not as good (in acircular cross-section) as the design with parallel plates in arectangular cross-section.

This particular concept of uniformly spread, small, identical capacitorsis applicable, not only to whole inner cross-sectional areas of pipesbut also to `bypass loops`, as previously described. A small areaconfiguration can be set at the center line of the pipe, or for thatmatter, anywhere within this cross-sectional area, if a particular spotof the inner cross sectional area is to be tested.

The present invention is not limited to pipelines at tanker terminals.The need for such monitoring or measurement may be required in inlandpipelines, refinery piping, and other similar applications. Theapparatus may also find use in the laboratory as well.

This innovative calibration method disclosed herein, eliminates the needfor physical separation of water from oil (the latter, is known to belengthy and cumbersome), and is applicable to laboratory or factorycalibration. Its reliability can be further improved by conductingmultiple injections at various water volume rates, in order to provideseveral equations for solving, more accurately, the unknown variableE_(oil), which is measured by the more conventional methods.

The present invention applies not only to liquids, but to an substanceand in any phase. An example of a liquid-gaseous mixture (which, is ofprime interest to the oil industry) is the steam injected into oil wellsfor enhanced recovery of heavy oils. It is important that the watercontent in the mixture be kept at an optimum value. Since the dielectricconstant of steam is exactly `1`, the contrast with the values ofdielectric constants of various waters, provides an incentive, byindustry, to utilize the method described herein. Additionally thismethod can be utilized to design steam quality probes either in surfacemeasurements or in downhole measurements, the latter, being commonlyreferred to as `well logging`.

What I claim is:
 1. An improved apparatus for detecting and calculatingbulk water content in steam comprising:a) a capacitor array, said arrayconforming to the cross-section of a duct used to transfer the steam,said capacitor array inserted in the steam duct; b) a capacitancemeasurement system; c) a means to calculate the water content of thesteam conveyed in said duct based on the measured capacitance.
 2. Theapparatus described in claim 1 wherein the duct used to transfer thesteam is formed with walls which are substantially at right angles toeach other and the capacitor array is a set of parallel plates withinsaid duct, said plates forming a plane which is substantially at rightangles to the longitudinal axis of said duct.
 3. The apparatus describedin claim 2, wherein the set of parallel plates occupies substantiallythe entire cross-sectional area of the duct.
 4. The apparatus describedin claim 1, wherein the duct used to transfer the steam has asubstantially circular cross-section and the capacitor array is a set ofconcentric plates within said circular duct.
 5. The apparatus describedin claim 4, wherein the set of concentric plates occupies substantiallythe entire cross-sectional area of the circular duct.
 6. The apparatusdescribed in claim 1 wherein said duct is positioned in the horizontalplane and further comprises at least one single element capacitorinserted upstream of said capacitor array and positioned at the bottomof the duct.
 7. The apparatus described in claim 6, wherein a secondcapacitor is used to measure the dielectric constant of the water. 8.The apparatus described in claim 7 wherein a third capacitor is used tomeasure the dielectric constant of the steam.
 9. The apparatus describedin claim 1 further comprising a temperature measurement system whereinthe measured capacitance is compensated based on the measuredtemperature of the steam.
 10. An improved apparatus for detecting andcalculating bulk water in steam comprising:a) a plurality of parallelplate capacitors for monitoring the electrical capacitance of steam in aduct used to transport said steam, said capacitors conforming to thecross-section of said duct; b) a capacitance measurement system; c) ameans to calculate the water content of water in the steam based on themeasured capacitance.
 11. The apparatus described in claim 10 whereinthe steam is placed in a duct formed with sides which are atsubstantially right angles and plurality of capacitors is a set ofparallel plates which form a plane which is substantially at rightangles to the longitudinal axis of the duct.
 12. The apparatus describedin claim 11, wherein the set of parallel plates occupies substantiallythe entire cross-sectional area of the duct.
 13. The apparatus describedin claim 10, wherein the steam is placed in a duct which has asubstantially circular cross-section and the plurality of capacitors isa set of concentric plates within said circular duct.
 14. The apparatusdescribed in claim 13, wherein the set of concentric plates occupiessubstantially the entire cross-sectional area of the circular duct. 15.The apparatus described in claim 10 wherein said duct is positioned inthe horizontal plane, further comprising a second capacitor, said secondcapacitor inserted upstream of said capacitor array and positioned atthe bottom of the duct.
 16. The apparatus described in claim 15 furthercomprising a third capacitor, said third capacitor inserted upstream ofsaid capacitor array and used to measure the dielectric constant of thesteam.
 17. The apparatus described in claim 15 wherein said secondcapacitor is used to measure the water content during the initialtransfer phase.
 18. The apparatus described in claim 10 furthercomprising a temperature measurement system wherein the measuredcapacitance is compensated based on the measured temperature of thesteam.
 19. An improved method of measuring and calculating bulk water insteam comprising:a) inserting a capacitor array in a duct used to conveysteam, said array substantially conforming to the cross-section of saidduct; b) measuring the capacitance of the steam conveyed in the duct; c)calculating the water content of the steam conveyed in said duct basedon the measured capacitance.
 20. The method described in claim 19wherein the bulk water is continuously measured and calculated.
 21. Themethod described in claim 19 further comprising measuring thetemperature of the steam conveyed in the duct.
 22. The method describedin claim 21 further comprising compensating the capacitance based on themeasured temperature.